The field of this invention is cooling apparatus for a turbocharged internal combustion engine that includes a turbocharger aftercooler. In a specific embodiment, this invention is especially useful for use in a diesel electric locomotive.
Diesel electric locomotives, used to move railway cars, are propelled by exerting torque to drive wheels that are in contact with rails. The power to propel the locomotive is developed first by a high powered diesel engine; and the diesel engine drives a generator that converts mechanical energy to electrical energy. The electrical energy is applied to electric traction motors, which convert the electrical energy back to mechanical energy applied to the wheels for propulsion along the rails.
As with all internal combustion engines, a diesel engine of a locomotive must be cooled in operation to remove heat developed in the combustion process so as to limit engine operating temperature. Although some heat may be removed by circulating lubricating oil, the major cooling is done by a primary engine cooling system using a circulating liquid coolant to carry excess engine heat from the engine to a heat exchanging apparatus such as a radiator for transfer to the environment. FIG. 1 shows, in block diagram, a prior art cooling system 10 used in a locomotive diesel engine 20. Coolant is circulated by a pump through a coolant conduit 24 from engine 20, from which it receives heat, to radiators 26, from which heat is released to the ambient air of the environment, which is drawn through radiators 26 by fans 28 and/or 30. The coolant is circulated by a coolant pump 38 through a coolant loop comprising coolant pump 38, coolant passages in engine 20, radiators 26, and optional oil cooler 34. Coolant tank 42 may be provided communicating with conduit 24 near the inlet of coolant pump 38 to give and receive coolant as required to maintain coolant in the loop.
In addition, the power of the engine can be increased by burning more fuel in the cylinder. To burn an increased amount of fuel, more air must be provided in the cylinder. In many modem internal combustion engines, including most used in diesel electric locomotives, this air is provided by a turbocharger 48, which compresses the ambient air to a higher pressure and therefore density. However, this compression also increases the temperature of the air, which is not desirable, since it reduces the volumetric efficiency of engine 20. In addition, a lower inlet air temperature can reduce undesirable emissions from engine 20. It is thus desirable to cool the air provided from turbocharger 48 to the cylinders of engine 20; and an aftercooler 22 is used to transfer heat from the air exiting turbocharger 48 to the coolant in coolant loop 10. Aftercooler 22 is placed in loop 24 in parallel with engine 20 so that the heat transferred to the coolant in aftercooler 22 is also radiated to the ambient air of the environment in radiators 26. The cooling of engine inlet air by aftercooler 22 thus improves engine efficiency and reduces engine emissions, as is also well known in the art.
The highest priority of an engine cooling system is the protection of engine components from temperatures beyond their safe operating limits. Thus, the system must be designed to provide a cooling capacity for the engine sufficient for the worst case expected: that is, the highest allowed engine power levels at the highest expected ambient air temperatures. Among the several parameters which affect the cooling capacity of the engine cooling system is the temperature difference between the coolant and the air entering radiators 26. The greater this difference, the greater will be the heat transfer from the coolant to the ambient air. Thus, the cooling systems of the prior art, as typified by system 10 of FIG. 1, are designed to maintain coolant temperature at or below a maximum temperature sufficiently low to protect the engine under the worst case conditions. When a cooling system is designed for a given maximum ambient temperature and maximum engine power level, the cooling capacity at radiators 26 will be more than required to cool the engine at lower ambient air temperature or at lower engine power operation; however, the unused cooling capacity of the main loop cannot be easily, if at all, applied to other cooling tasks, such as aftercooler 22, in an optimal manner.